The present invention relates to a pneumatic sander structure which is able to prolong using life of the bearing and will not interfere with the operation of the grinding mechanism.
A conventional pneumatic sander employs a pneumatic driving mechanism which has a shaft for driving an eccentric block of a grinding mechanism to rotate. The eccentric block further drives a grinding disc at the bottom end thereof to rotate. An annular groove is formed on the lower bearing seat, in which a slightly elastic rubber dustproof cover is fitted. The dustproof cover is a hollow body. The lower end of the vertical circumferential wall of the dustproof cover is tapered so that the vertical circumferential wall has an inward inclined lower end. The vertical circumferential wall is fitted around a flange of the lower bearing seat. The bottom end of the inclined circumferential wall is positioned at a position spaced from the vertical face of the middle portion of the eccentric block by a gap. The angle edge of the inclined circumferential wall slightly touches the top face of the eccentric block to define a space between the eccentric block and the dustproof cover. When the eccentric block is rotated relative to the outer housing and a strong revolving air flow is produced, the space is prevented from being disturbed by the air flow so that the grinding powder will not escape into the lower bearing.
Referring to FIG. 6, a clearance exists between the lower bearing seat 81 and the shaft 82 and the bearing 83 has a gap for ventilation. Therefore, the high pressure air for drivingly operating the pneumatic driving mechanism will flow through the clearance between the lower bearing seat 81 and the shaft 82 into the lower bearing seat 81 and flow through the bearing 83 into the space inside the dustproof cover 84. The air will then flow out through the gap between the angle edge of the inclined circumferential wall 841 of the dustproof cover 84 and the top face of the eccentric block 85. When the air is exhausted, it will exert a pushing force onto the slightly elasitc dustproof cover 84, making the inclined circumferential wall 841 thereof contact with the top face of the eccentric block 85. Therefore, the angle edge of the inclined circumferential wall 841 will be continuously abraded by the top face of the eccentric block 85. This slows down the rotational speed of the eccentric block 85 and the inclined circumferential wall 841 is worn out to enlarge the gap between the angle edge and the top face of the eccentric block 85. As a result, the powder will intrude into the bearing 83 to affect the using life of the bearing 83.
It is therefore a primary object of the present invention to provide a pneumatic sander structure in which the dustproof cover is disposed between a top face of the middle section of the shaft and the bearing in the lower bearing seat. The outer edge of the dustproof cover upward extends to the lower bearing seat and is kept spaced therefrom by a very small gap. Therefore, the air flowing into the lower bearing seat can be exhausted, while the powder produced outside the dustproof cover during grinding operation is prevented from entering the bearing of the lower bearing seat. Therefore, double effects of no interference with the operation and prolonging using life of the bearing can be achieved.
According to the above object, the pneumatic sander structure of the present invention includes a housing, a pneumatic driving mechanism and a grinding mechanism which are disposed in the housing. The housing has an air incoming way and a air outgoing way. The pneumatic driving mechanism has an annular wall in which a rotary body with vanes is placed. The annular wall is formed with inlets and outlets for rotating the rotary body. An upper and a lower ends of the annular wall are respectively connected with an upper and a lower bearing seats having bearings therein. A shaft is fitted into the rotary body and the two bearings. A bottom end of the shaft is an eccentric block of the grinding mechanism. A top end of the eccentric block is a middle section coaxial with the shaft. A hollow dustproof cover is disposed between the middle section and the lower bearing seat. The dustproof cover is positioned between a top face of the middle section and the bearing in the lower bearing seat. The dustproof cover is fixedly clamped by the top face of the middle section and an inner ring of the bearing. The dustproof cover is formed with a recess corresponding to the outer ring for avoiding unnecessary abrasion. An outer edge of the dustproof cover upward extends to a lower bottom face of the lower bearing seat and is kept spaced therefrom by a very small gap.
The present invention can be best understood through the following description and accompanying drawings wherein: